This invention relates to an angular position detector of a rotary shaft and more particularly to an angular position detector mounted within an engine ignition distributor for detecting an angular position of a rotary shaft.
FIGS. 1 and 2 are schematic views illustrating main portions of one example of an angular position detector apparatus disposed within an engine ignition distributor to which the present invention can be applied. It is seen that a rotary shaft 2 which rotates in synchronization with the unillustrated internal combustion engine is disposed at the center of a housing 1. The rotary shaft 2 has integrally mounted thereon a disc 3 shown in FIG. 2 having two sets of a predetermined number of through holes or apertures 31 and 32 arranged in two arrays along the circumferential direction. In the housing 1 and on one side of the disc 3, two light-emitting elements (not shown) corresponding to the respective arrays of the apertures 31 and 32 are provided, and on the other side of the disc 3, detection elements 41 and 42 such as photo-diodes for generating a detection signal corresponding to the angular position of the rotary shaft 2 in response to the light which has passed through the apertures 31 and 32 are provided. The detection element 41 has an output terminal which is electrically connected by an electrical conductor member 5 to a processing circuit 6 which is made of IC chips, for example.
In the angular position detector as above described, when the disc 3 is driven by the rotary shaft 2 connected to the unillustrated engine, the detection elements 41 and 42 receive intermittent light from the unillustrated light-emitting elements passing through the apertures in the disc 3. Then the angular position of the rotary shaft 2 can be determined by processing the output signals from the detection elements 41 and 42 by the processing circuit 6. The angular position thus obtained may be used as a reference angular position for controlling the engine ignition timing.
In the angular position detector of the above-described construction, the conductor member 5 which is embedded in the cast-molded resin is at a position close to the inner peripheral portion of the housing 1 which is close to the rotary shaft 2. However, the rotary shaft 2 and the disc 3 may have induced therein a high tension voltage due to igniting. Therefore, the angular position detector as above described in which the input signal conducting conductor member 5 which is of a high impedance and a high sensitivity is positioned close to the rotary shaft 2 and is easily undesirably affected by the above-mentioned high tension voltage, resulting in an erroneous operation of the detector.